This invention relates to an improved filter aid material. More particularly, this invention relates to the composition and preparation of an improved filter aid comprised of expanded comminuted pumicite particulate. These particulates are to be used for clarifying and dehydrating the soiled solvent used in drycleaning operations.
Heretofore, the solvent used in drycleaning operations has been clarified and dehydrated by various means such as processes of filtration, the use of precipitation by various chemical reagents, or diassociation. Various experimental tests have shown, however, that in practically no case is the effluent perfectly free of moisture and foreign matter. Thus, the "washing" of the solvent results in only a partially clean solvent and, hence, subsequently there may be only a less than optimal drycleaning accomplished because the solvent itself is not free of foreign matter. Also in the past, various experiments and practices have endeavored to use centrifugal separators in order to separate suspended impurities and moisture. It was found, however, that a gelatinous residue would remain, this being formed by the moisture in the goods being cleaned emulsifying with a percentage of the soaps and oils liberated in numerous cases with the soap used in drycleaning. The residue would hold finely divided solids matter in colloidal state and removal of such residue by mechanical means was found to be substantially impossible.
Other improvements in the process of "washing" the solvent used in drycleaning operations has included the use of diatomaceous earths and compositions of diatomaceous earths which are constructed to filter the cleaning solvent. These compositions commonly are known to have various adsorbents prepared in conjunction with the diatomaceous earths and commonly include alumina, metal silicates, ground or fiberous asbestos, metal stearaets, sawdust, cellulose powder, starch and/or various powdered synthetic polymers.
In more recent times, commercial filter aids have been manufactured from particulates of naturally occuring glass of igneous origin that will expand when heated to yield a light, cellular particle. The heated and expanded form of this particulate is commonly known in the trade as "perlite". In strict geological usage, this term is restricted to a single variety or specie of volcanic glass. Perlite usually is brittle and friable. It rarely has a silica content greater than 70% and a combined water content is generally present in the range of 2 to 5%. Technically, acid volcanic glasses containing less combined water than perlite are classed as obsidians, and those containing more combined water are classed as pitchstone.
The manufacture of perlitic particles requires their introduction into a flame so as to cause expansion under a controlled temperature in the range of 1600.degree. F., the subsequent softening of the glass being coincidental with the volatilization and release of the combined water causing the particles to quickly expand or puff up to an aggregate many times their original volume. However, dependent upon it's origin, the perlite minerals differ markedly in the time and temperature necessary for expansion, the controlled temperatures varying generally between 1400.degree. and 1900.degree. F. Likewise, the relative chemical constituancy of naturally occuring perlite is extremely variable with a wide range of temperatures necessary to accomplish expansion of the particulate. Due to the inconsistant and variable range of chemical composition in naturally occuring perlite, the ultimate particle that is produced is very inconsistant insofar as it's reliability for the purpose of solvent cleaning is concerned. It has been found, for example, that perlite, though being inconsistently satisfactory as a filter, that the clarity of the filtrate is inferior to the clarity of the filtrate obtained when other types of filter aids are used. Moreover, perlite filter products produced to date have been characterized by their inability to function as high flow rate filter aids. As a result, it is the common consensus that they have generally been commercially rejected in the drycleaning industry as an effective and reliable filter aid.